Saw-tooth wave generator



SAW-TOOTH WAVE GENERATOR Filed June 6, 1951 /NVf/V TUR A 7' TORNEY Patented Sept. 29, 1953 V,2,654,050 vsAWL-'rooTHWAvE GENERATOR -Wolfgang Reinhardf Pforzheim,

Germany, as-

signorl to international Standard'Electric Corg poration, Delaware New York, N. Y., a` corporation of Application June 6, 1951, Serial Nol 230,098 InrGcrmany June 2.4, 1950 I 1 Anraim. (Cl- 315-27) fThe- `present `invention relates to acrcuit arrangement for,` generating fs awtooth curr/ents such asl are usedffor energizing-*the deflection coilsY of television or lother cathode-ray tubes. A More particularlyfthe invention relates to a saw-tooth current. generator in which a sawtfooth voltage, produced by slowly charging a `condenser and rapidly discharging it, orvice versa., 'is' fd to-the gridof a tube, to the-p'latelcrcuit of-fwhich thedection coilsy are coupled either'directly or' "through a transformer. vCircuit arrangementsof tliistype are-most advantageou'sl in cases wlflere -thetime constant of the deflection coil' is small compared to the period of the saw-tooth wave; as', for example, in television J vertical deflection circuits.

lfA'n"saw-tc'iotli wave lobtained in this 'manner has a certain curvature, evenwhen vthe condenser voltage is linear. ""This 'cur-rature results from curvature of the tube characteristic and also rntheindctance A'of the output transformer, which'is 'connected across" the 'deflection con. 'rhe'crreht ncwing through" the' deflection eil resistance wilrhave' asaw-'too'th' shape, and a corresponding"saw-teeth voltage u1;v will he present u"across jthe fr"transforlner, 'through which, thereffre; a'-'-paabo1icc'urrent if; must new, for since l zLfuLdt futis proportonal't t; iL 'must be proportional to t2. "ilins, 'the 4'output'tube"inustroduce a composite current" which is iinitely not Saw;

toothed but which may have a minimum` within must'ccur. The control vitagejon the grid of i 2 Y Vthe primary side of the transformer, ucthe'condenser voltage, lc the negative feedback' factor, and v the gain, we may write the following vIrelationship:

us="(uc `k.us) which becomes:

It is seen from this that `when o.7c` 1," the c'il voltage depends almost-solely on thecondnser voltage and that with a linearly ncreasingcondenser voltage an almost linearly increasing dee flection current is obtained.

However, one drawback of this inverse voltage feedback is the vsmall internal resistancel of 'the circuit. The defie'ction coil inductance offersa certain amount of opposition tothe rapid'return of the deflection current, whichjmust-complete its retrace in about 5%'of the time takefffor the trace. This effect is more pronounced when the ohmic resistance in serieswith'the inductance is lower, and hence when thetimeconstant' L/R is greater. In order tomake ysure 'that the'retrace will jtakef place' withinl the zspecified time it istherefore necessary to add wpulsevitage te the denectingtous,l ofthe grid tf the amplifier feeding sadcoils,

AfIn Vorder 'to overcome "this"`diculty; it Vis'p'roposedaccording to theinvention, riot-to ake the f negative 'feedback dependent onthe Ivoltage ofithe'dee'ctng coils but `ratifier `to n'ake'the feedback voltage vary proportionally fto''the' de'- ecting'coil current. Y

Accordingly, a primary' object "of the present inventionis lthe generation' "of linear' sau/tooth currents having ashort-retrace'period.

Another objectof thel irivelltion is y'tolinear-im the? output of a savvtothr Ic'urrentfl'fgenerator without increasing 'the` timeconst'antoff'sad gene erator.

:Another-object 'of' the invention v@isf toy provide an energizing c'ircuit' foriv deiiection. fcoils'ofi'. a cathodeg'ray tube, 1in which circuit noniinearities ofr'bothv the saw-tooth current fcrnisaid'f nentetion coils and of the saw-tooth driving'fvitage arezompensated.

Other objects and advantages of thelinvention will become apparent :from-the following description of. particular embodiments thereof illustrated inthe drawing,' v wherein:

fFi'g. liis a circuit diagram-*of 'one' embodiment of theinventio'n; n U

rigs. 2 and :sT-'show embodiments ofthe-invention providing compensation for both the sawtooth voltage and saw-tooth current; and

Fig. 4 shows still another embodiment of the invention in which the compensating circuit is in the cathode circuit of the current amplifier.

Various examples of the invention are shown in the several figures of the drawing. In all of the figures the reference numeral I denotes the deflection coils; numeral 2, the output transformer; 4, the amplifier tube; 5, the coupling condenser; 6, the grid-leak resistor; 1, a resistor across the coupling condenser; 9, the charging condenser; III, the load resistor; I I, the blockingoscillator transformer, and I2, the blockingoscillator tube. Condenser 9, resistor III, transformer II, and tube I2 make up a well-known blocking oscillator arrangement, in which the condenser periodically undergoes a slow discharge of a negative potential thereon and is then charged negatively again by the grid current. Resistors and 1 form a Voltage divider that makes possible the correct location of the operating point of tube 4.

In Fig. l the inverse-feedback voltage, which, according to the invention, is proportional to the deflection current, is produced by connecting in series with the deflecting coils I a resistor I3, across which is connected the primary winding of the feedback transformer. In this manner, the following advantages are obtained. The feedback voltage is no longer a function of the voltage on the deecting coils but rather of the current passing through the latter, i. e., a change in coil voltage causes practically no change in coil current. The internal resistance of the circuit is thus increased. This, however, decreases the'effective time constant of the deilecting coils, so that the deflection current can be made to complete its return within the prescribed retrace time without need of introducing any additional pulse voltage. The disadvantage of this arrangement is that the inverse-feedback voltage becomes very small because the ohmic resistance of the deiecting coils is very small and the series resistor I3 must accordingly be chosen small. .ff

Fig. 2 shows an arrangement in which an'inverse-feedback voltage proportional to the deflection current is obtained through the -use of an additional transformer 3, having its primary winding connected in series with that of the output transformer 2. In order for the feedback transformer 3 to have the same linearizing effect during the entire trace, its voltage must vary in the same way as the voltage on the deecting coils. parallel with the secondary winding of transformer 3, a resistance 8, which, together with the inductance of the secondary winding, gives the same time constant as the resistance of the deflecting coils I taken together with the induct- Iance of the parallel-connected transformer -2.

The effective voltage on the grid of tube 4, Fig. 2, is proportional to the sum of the voltage across condenser 9 and the voltage developed in the secondary winding of transformer 3, which is of such a polarity as to oppose the condenser voltage.

The rate of change of the voltage on condenser 9 is and therefore it is dependent on the charging current i. This current, in turn, depends on the voltage across charging resistor II). In order to minimize the variations in this voltage, thus This is accomplished by connecting in making the voltage on the condenser 9 as linear as possible, it is further proposed, as shown in Fig. 2, to insert the secondary winding of transformer 3 between charging condenser 9 and the charging resistor I0, for then the lower end of resistor I0 will be at a point whose potential changes substantially less.

In order to eliminate any remaining nonlinearity when a smaller feedback factor is used, it is further possible, as shown in Fig. 3, to insert a winding I4 between the charging resistor I0 and the plate potential line. Winding I4 is coupled to one of the transformers in the plate cir-cuit of tube 4, for example output transformer 2, and is so designed and polarized that the voltage on charging resistor Il) is approximately constant. In other respects, the circuit of Fig. 3 is similar to that of Fig. 2 and hence needs no further description.

Instead of feedback transformer 3 of Figs. 2 and 3, a coil I3 can be connected in the cathode -circuit of tube 4, with a resistor 8 bridged thereacross, as shown in Fig. 4. The time constant of the circuit made up of coil I3 and resistor 8 is again made equal to the time constant of the resistance of the deection coils and the parallel inductance of transformer 2. It will be understood that the elements 8 and I3, being common to the grid and plate circuits of tube 4, provide a degenerative feedback voltage from the plate circuit to the control grid or input circuit of tube 4. This feedback voltage will vary with the platecurrent of tube 4, and will be substantially proportional to the current through deflection coil I, since the circuit 8, I3 has the same time constant as the deflection coil circuit. Other portions of the circuit shown in Fig. 4, being similar to the circuits of Figs. 1 to 3, need not be described again.

It will be obvious to those skilled in the art that various changes may be made in the embodiments of the invention described herein. It will be apparent, for example, that the negative feedback circuits shown in the several gures of the drawing may be substituted one for another, or may be incorporated in the same circuit. It will also be apparent that any suitable source of sawtooth voltage may be used in place of the blocking oscillator circuit shown herein and that other modifications of the circuits illustrated and described herein may be made without departing from the principles of my invention as set forth in the claim.

I claim:

A generator of sawtooth current waves comprising means for generating a sawtooth voltage, said means including a charging circuit having a resistor and condenser connected in series, an electron tube having a control grid, cathode and anode, an input circuit connecting said control grid and cathode across said condenser, an output transformer and an inverse feedback transformer having primary windings connected in series in the anode circuit of said tube, a cathode ray tube deflection coil connected across the secondary winding of said output transformer, the secondary winding of said inverse feedback transformer being connected in said input circuit and in series with said resistor and condenser of said charging circuit, a resistor connected in parallel with said last named winding and forming therewith a circuit having a time constant substantially equal tc the time constant of the circuit formed by the deection coil Iand. the secondary winding of the output transformer.

WOLFGANG REINHARD.

Number Name Date White Apr. 28, 1942 Dome May 26, 1942 Foster June 8, 1948 10 Boadle July 13, 1948 Schade Apr. 12, 1949 Richards Apr. 19, 1949 Number 6 Name Date Kerkhof May 31, 1949 Wolf .June 21, 1949 Bocciarelli Sept. 20, 1949 -Kerkhof Apr. 11, 1950 Gannaway et al. Sept. 5, 1950 Schwarz Feb. 27, 1951 Edelsohn Mar. 13, 1951 Court May 15, 1951 Montgomery July 24, 1951 Parker July 24, 1951 Reeves Aug. 7, 1951 Court Nov. 6, 1951 

